Kind of a silly post, and not very scientific, but we are sticking to it. During our check in today we discussed Mariner suspension frame design concept, and we chose to proceed with MOS-style (4 posts, rectangular footprint).
- We looked at a scaled-up SOS (WIP, lots of things broke, just notice the larger side plates and base - see Attachment 1) and we were not super excited by the aspect ratio of the larger side plates - didn't look super stiff - or the mass of the base.
- We noted that the intermediate mass will need OSEMs, and accommodating those will be easier if there is a larger footprint (as afforded by MOS).
MOS-style it is, moving forward!
Also, Checked In to PDM (see Attachment 2 - filename 40mETMsuspension_small-shields.SLDASM and filepath \llpdmpro\Voyager\mariner 40m cryo upgrade ) the current state of the Mariner suspension concept assembly (using MOS). Other than updating the test mass to the 6" configuration, I didn't do any tidying up, so I'm not perfectly satisfied with the state of the model. This at least puts the assembly in a place where anyone can access and work on it. Progress!
All parameters are temporary:
Test mass size: D150mm x L140mm
Intermediate mass size W152.4mm x D152.4mm x H101.6mm
TM Magnets: 70mm from the center
Height from the bottom of the base plate
- Test mass: 5.0" (127mm) ==> 0.5" margin for the thermal insulation etc (for optical height of 5.5")
- Suspension Top: 488.95mm
- Top suspension block bottom: 17.75" (450.85mm)
- Intermediate Mass: 287.0mm (Upper pendulum length 163.85mm / Lower pendulum length 160mm)
- IM OSEMs: Top x2 (V/P)<-This is a mistake (Nov 3 fixed), Face x3 (L/Y/P), Side x 1 (S)
- TM OSEMs: Face x4
- OSEM insertion can be adjusted with 4-40 screws
- EQ Stops / Cradle (Nov 3 50% done)
- Space Consideration: Is it too tight?
- Top Clamp: We are supposed to have just two wires (Nov 3 50% done)
- Lower / Middle / Upper Clamps & Consider installation procedure
- Fine alignment adjustment
- Pendulum resonant frequencies & tuning of the parameters
- Utility holes: other sensors / RTDs / Cabling / etc
- Top clamp options: rigid mount vs blade springs
- Top plate utility holes
- IM EQ stops
Discussion with Rana
- Hoe do we decide the clear aperture size for the TM faces?
- OSEM cable stays
- Thread holes for baffles
- Light Machinery can do Si machining
- Thermal conductivity/expansion
- The bottom base should be SUS... maybe others Al except for the clamps
- Suspension eigenmodes separation and temperature dependence
# Deleted the images because they are obsolete.
Some more progress:
- Shaved the height of the top clamp blocks. We can extend the suspension height a bit more, but this has not been done.
- The IM OSEM arrangement was fixed.
- Some EQ stops were implemented. Not complete yet.
Does this work? Is this insane?
Today we looked at possible locations for where we will be setting up Mariner Suspension and Cryo chamber. The first option was the far left table in the CAML lab but it seems that there is going to be an issue with height clearance, so we have come up with another solution which takes a table from Koji's lab which is 3'x4' ft and moving it into CAML lab in the back right of the lab. To move the table we may need to call facilities to help us because we will most likely need to take the table apart to get it out of the lab. The aisle space in Koji's lab is about 43 inches, but the doorway, which is the tightest space, is 35 inches.
After we have set up the table in CAML we are planning on moving the Chamber in DOPO-lab to CAML. We plan to use skyhook with has a load limit of 500lbs/227kg this should be more than enough to move the chamber. We still need to get the wheeled base for skyhook we are in the works in doing so.
Also, We want to remove the previous setup from the chamber and leave it at DOPO-lab. Stephen is going to figure out how to keep it clean (sort of). Besides these transportation logistics, I am also working on the electronics as an immediate task and the electrical arrangement in the chamber.
to do list
- Check the table height
- Check the chamber height (base/cap)
- Check how much the chamber cap needs to be lifted (so that we can remove it)
- Is the weight capacity sufficient?
- B246/QIL Skyhook
- OMC Lab
Table moving effort in the OMC lab: See https://nodus.ligo.caltech.edu:8081/OMC_Lab/412
Ongoing points of updates/content (list to be maintained and added)
Mariner Chat Channel
Mariner Git Repository
Mariner 40m Timeline [2020-2021] Google Spreadsheet
For our optical contacting, Jennifer and I are starting out with glass (microscope slides), with the setup in the EE shop next to the drill press (photos from Jennifer to follow).
Some interesting links:
This was performed last Friday (7/8).
I secured a thermocouple perpendicular against the hotplate and recorded the maximum temperature the hotplate reached at Low, Medium, and High. It took about 5 minutes to reach a stable temperature, where stable means that the temperature stayed within +/- 0.5°C for a minute. The hotplate maintains a certain temperature by turning itself on and off, so the temperature would drop slightly (at most, a few °C) while the hotplate was off. The maximums were:
At the max temperature, I moved the perpendicular thermocouple around to roughly find the variation in tempearture at different locations on the hotplate. Facing the nob, the top right quadrant is about 10-20°C cooler than the other quadrants, which are within 5°C of eachother. Excluding the cooler quandrant, the center and the outer edge are within 5°C of eachother. The temperature increases as one approaches half the radius, with it being about 20-40°C greater than the center and outer edge. The highest recorded temparture was 289°C at half the radius in the bottom left quandrant. This was only meant to be a rough test to see how even the heating is.
Note that the slides have "GLOBE" printed on one side. I always bond the opposite using the opposite side without the text.
On Monday (7/11), I began experimenting with bonding, starting with "air-bonding," which is trying to make dry, gently cleaned slides stick. I achieved my first succesful optical contact with what I call "acidental water-assisted direct bonding" or "water-bonding," where I accidentally clasped two wet slides together while washing my dirty finger prints off them. After the accidental discovery, I repeated it by running water over the slides while there were clasped together and achieved the same result. After a few hours, I attempted partially sliding apart the second water-bonded sample. I could slowly push them apart by pressing my thumbs against the long edge, but it took quite a bit of force. I decided to let 4 samples sit overnight: 1 air-bonded, 1 air-bonded with the brass hunk on top of it, and 2 water-bonded. Neither time nor pressure improved the air-bonded samples as they still slid apart very easily. The first water-bonded sample slid apart easier, but one part remained stubornly attached until I began shaking it violently. The second water-bonded sample was much harder to slide apart than the last time I tested it. With all the force of my fingers, I could barely make it budge.
Note that I am just testing out different techniques, so I have not set up the thermocouples to precisely measure the temperatue.
On Tuesday, I developed a new method of putting water, isopropanol, or methanol on one slide then squishing the other slide on top of it to fill the gap with the afformentioned liquid. The slides are slippery at first, but as they dried, which took about 15 minutes, the bond forms. The bonds were strong enough that I could just barely push the slides appart by applying pressure to the side using my thumbs. I prepared 4 samples this way, 2 with iso and 2 with meth. I took one of each and heated them on Medium for 30 minutes under the brass hunk with the aluminum square on the bottom and copper foil on both sides of the samples. Earlier in the day, I tried heating them without the weight on top, but the heat just broke the bond. I took the remain two and set them aside as controls.
On Thursday, I returned to check the bonds. The heated samples had broken. I intented to check on Wednesday, but I was sick from food poisoning, so I do not know whether the bonds broke immediately after heating or due to sitting for an extra day. For the control samples, one also had a broken bond, but the other had become even stronger.
I noticed that, when the slides are successfully bonded, the shape and appearance of the Newton's rings change, which can be seen in the pictures. I speculate that the circles on the unbroken control are the bonded regions. Ideally, we want to see no Newton's rings.
I have found that, after cleaning the glass with methanol (or even sometimes with just a dry lense-cleaning cloth), I can get glass slides to bond by rappidly rubbing them together until something sticks. This was inspired by watching "Wizard of Vaz" perform bonds on YoutTube. While cleaning, I now use enough strength to make the glass squeak, as advised by him.
Upon heating, I encountered the same issue as when I bonded them by putting a liquid (water, methanol, etc.) in the gap, which leads me to now believe that the broken bond is not due to the expansion of a liquid. Further, even at the low temperature of 60°C, placing the liquid-less sample on the hotplate breaks the bond in seconds, which I caught on video. In the attached video*, you can see that, before the heat, the bond is strong enough that I cannot push it appart with my fingers, but after the heat, it slides easily. Note that, outside of taking the video, I always lay the entire slide on the center of the metal so the sample is evenly heated.
*This is my first time attaching a video. If it didn't attach properly, I'll add it on to a later log. I also want to record myself performing the rubbing bonding technique.
Yesterday, I did two rounds of slowly heating 4 samples to the maximum hot plate temperature. This was to formally test if my success with a single sample earlier in the week was a fluke. Note that the hot plate takes about 10-15 minutes to reach a stable temperature when it is turned up one notch.
I bonded 4 samples by putting methanol in the gap between the glass slides and letting it dry to create a gap.
Starting at room temperature, I heated the slides on each setting for roughly 15 minutes, then let them cool down naturally over the course of an hour. 3 broke broke at medium heat, and 1 survived the whole process. I belive these broke because the bonds were weaker and I heated them slightly too quickly. In previous tests, I would manually switch the hot plate on and off, but I wanted to see if the hot plate could heat up slow enough on its own.
I bonded 4 samples by scrubbing the slides with methanol, using a compressed air duster to blow off the fibers, rubbing them together with the pressure of my fingers, and repeating this whole procedure until they stuck (it took 2-4 repeats).
Starting at room temperature, I heated the slides on each setting for exactly 20 minutes, then let them cool down naturally over the course of an hour. All of them survived to the maximum temperature (the pictures show them at the start and end of the heating, note the temperature). I credit this to the stronger bonding proceedure and the extra 5 minutes for them to adjust to the temperature. I did not turn the hot plate on or off at any point, I just let it heat up at its own rate.
I cannot tell if the bonds are stronger. The size and shape of the Newtons rings did not change.
We succeeded in setting up an apparatus for quantifiying the razor blade test. After mounting the glass slides such that the razor edge rested against the gap, we slowly turned the knob to push the blade into the gap. We started with the knob at 0.111, and at 0.757, the bond between the glass slides failed. As we approached 0.757, the interference pattern in the glass shifted, foreshadowing the break.
(Edit by Koji. This 0.757 is 0.0757 I suppose...? And the unit is in inch)
Pictures of the razor test apparatus before and after disassembly, to make future reassembly easier.
While finalizing my work plan for the quarter, I decided to look at the Thor Lab slides. This was instructive because they highlighted the troubles I will have with working with silicone. They are fragile and their small, thin sizes makes cleaning and manipulating them (without contamination) much more difficult compared to the glass sides from before.
I tried cleaning and bonding them the same way as the larger slides. Rubbing them together did not work like with the larger sides, but that may also be a function of being more careful, as not to break them. Once I cleaned them, it only took a tap from my finger to get the center to bond, but the bonded surface area still did not spread out like it did in the YouTube videos (http://youtu.be/se3K_MWR488?t=80). By pressing down around the bonded area, I could expand it slighty. Note that I did crack one slide in the process of doing this, as shown in the pictures.
Because the slides are so thin, I think they will benefit greatly from being left under a heavy object, although it may be difficult to put the weight on the slides without them breaking.
Continuining with my casual exploration of the Thor Lab slides, I heated them from off --> low --> med --> high, with 10 minutes on each setting. The only pressure I applied was 3 larger glass slides, and that was only to flatten out the copper that the smaller, bonded slides sat on top of (so the contact with the heating plate was even).
The heat made the bonded area smaller, but it did not break. As the slides cooled, the bond area increased slightly but not back to the original size. Next I will try this with slower heating and additional pressure.
Given that these glass slides are much thinner than the ones I worked with prior, I suspected they would be more receptive to pressure. I decided to replicate the tests I performed with the larger slides: I prepared 8 samples, 4 by smushing the slides together with methanol in the middle and another 4 by cleaning the slides with methanol before pressing them together with my fingers. I put 2 of each type under the cylindrical weight, and 2 of each type under the rectangular weight with the addition of heating. The heating consisted of switching the temperature from off --> low --> med --> high with 15 minutes on each setting.
I will check the results in the morning. I need to wait until the rectangular weight is completely cooled, otherwise I cannot remove it from the hot plate in manner that does not risk cracking the glass.
The first sample picture shows the pressed slides on the top and the smushed slides on the bottom. For the second picture, this is reveresed. Correction: the order is the same for both samples.
These are the results from the previous log.
At long last, there was an improvement with pressure and heat! Pressure without heat and pressure with heat both showed a small improvement. Although the improvement was not major, it does show that pursuing this method of adding weight and heat are viable. Since this was a test, I put less weight on and heated it fast than intended, but now I feel confident to add more weight and slower/greater amounts of heat.
Before jumping to conclusions based on my previous results, I wanted to check that it was indeed heat and pressure, not time, that led to the bonds improving.
I prepared 4 samples, all with my standard pressing technique (which still leaves room for improvement). 2 samples will simply be left to sit undisturbed, and the other 2 will be left under both (rectangular and cylindrical) weights. I will check these in roughly 24 hours, just like the last test.
The 2 slides on the right are the ones under the weights.
I was unable to check the samples because I could not get access to Bridge, so they will be checked tomorrow and the results will be added as an edit to this log.
Given that I was unable to do work in the lab, I instead began a second attempt at writing code for the Arduino to use PWM to control the hot plate temperature.
As expected, the suface area of the bond only increased for the samples under the weights. I did notice something worrying: one of the non-weighted samples actually had its surface area decrease. It is unclear if this is a one-time thing or if all of the bonds deteriorate with time. Unrelated, but I also noticed that the bonded areas always have small dots that refuse to bond. It's unclear if that is due to imperfections or contamination (I suspect the latter).
I left all 4 samples under both weights out of curiosity to see if the bonded surface area would increase further (or possibly decrese further).
I wrote a program to control the heating rate of the hot plate using Pulse Width Modulation (PWM), and it was a great success!
For roughly 6 minutes, the hot plate was power cycled with a rate of 100 ms on followed by 900 ms off. Based on my calculations, this should correspond to a 0.08°C/sec temperature increase. In other terms, we expect a 24°C increase in the span of 5 minutes. For comparision, without PWM, the hot plate heats up roughly 100°C in that same timespan. I recorded the temperature by filming a thermometer and transcribing that video into a text file, which could be analyzed and graphed. I only transcribed the first 5 minutes of the 17 minute video (I also filmed part of the cool down) because 5 minutes was enough to show clear results.
At t=0, the hot plate was 21.4°C, and at t=300, the hot plate was 49.7°C. That is a 28.3°C increase in the span of 5 minutes, only 4.3°C higher than the predicted value. The rate, 0.094°C/sec, is only slightly faster than the desired 0.08°C/sec. Further, as shown in the graph, the temperature increase was almost perfectly linear, which is ideal. Overall, using an Arduino to PWM the hot plate is looking very promising.
I repeated the first test, but let the hot plate run longer. It revealed that the linearity for the lower temperatures completely falls apart at the higher temperatures. I think it should be fairly straightforward to modify the code to accommodate this.
The previous test was cycled with 0.3s on follwed by 0.7s off*. This test was 0.7s on followed by 0.3s off. I intended to let it run longer, but I accidetly knocked the thermocouple over while trying to move the cable father from the hot plate so the plastic would not risk melting.
Like before, we see that it starts out relatively linear. I noticed the heating light kind of fluttering around 200°C which appeared in the data as a small decrease around 450s on the graph. I do not know the source of this issue, but I fear it may be the hot plate overriding my cycling with its own built-in cycle; something left for future testing. This is the last data I will gather using v1 of my Arduino code, as am I now working on implementing what I have learned in a smarter v2 of the code. I included v1 of the code, and the txt files for the first three tests.
*I think. Could have been 0.1 on, 0.9 off. Note to self: double check this.
I had a little set back regarding the non-linear portion of the heating. After about 150°C, if the heating rate is kept constant, the heating graph transitions from linear to logarithmic. I was able to show graphically that, yes, it is indeed logarithmic, but I could not think of an algorithmic way to translate this logarithmic curve into the increase in heating rate to maintain a linear heating rate. I do have some ideas which I will test tomorrow.
I had some trouble with the code not working as intended (partially because it has been I while since I coded in C++). However, I was able to run two tests with the new code, although I ran out of time to type up the data for the 2nd. Graphing the 1st test's data, it appears that my improved code is an improvement, but the heating is still slowing down as it approaches 200°C. I need to re-run this test, but with v1 of the code, for better comparison.
The hot plate was supposed to increase 180°C in 10 minutes (so that I would reach 200°C), but due to an inscrutable bug, it did not exit the while loop, so it continued past 10 minutes.
For the following two graphs, I ram four tests: two using the the v1 of the PWM code and two using v2 of the PWM code. The graphs show the heating rate I was aiming for and the actual results. It turns out, my v2 does not work better than my v1. Before 150°C (which is where I believed that (assuming the rate is kept constantly) the heating rate shifted from linear to logarithmic), v1 is an overshoot and v2 is slightly less of an overshoot. The goal of v2 was to increase the rate after 150°C to compensate for this drop off, but it does not appear to have worked.
While I would still like to refine my code, I think it will be good enough to try using it to actually heat the samples.
Before trying the PWM on actual samples, I wanted to make one final attempt at improving my code (labled as v2.1). This change appears to have 1) broken the code regulating the basic heat cycling process 2) caused the hot plate to heat up far, far too quick. Since the thermometer strangely turned off halfway through, I only have two pictures as evidence that this test existed: a screenshot of the Arduino program telling me that the max cycle rate had been reached (which should have not happened) and a frame from the video filming the thermometer showing the peak temperature (which is 100°C high than expected). Somehow the hot plate reached over 300°C, which I thought was impossible because the hot plate's built-in heat cycle should have kicked in around 260°C. Unrelated, but I am performing this test in my dorm room because I was quarentined due to COVID exposure, and I like using my personal fan and the house's freezer to cool down the hot plate quicker.
I made some adjustments (labled as v2.2), and I had the same failure as v2.1, except I managed to capture it on camera.
Finally, with v2.3, I managed to fix all the issues. I ran out time today to transcribe the temperatures for graphing, but this itteration of the code managed to reach 200°C in 10 and 7 minutes for test #1 and #2, respectively. I also managed to fix the problem of the hot plate not turning off after the desired heating time. The real test will be trying a slower heating time, like 20 minutes, but I am glad I postponed using actual samples because this fix has given me code that appears to work exactly as I hoped.
Here are the graphed results from yesterday's tests, both by themselves and overlayed with the previous tests. I am satisfied with my code; it has given me the (roughly) linear heat increase that I desired. The only last thing I would like to test is heating over a signficantly slower time.
I tried increasing the temperature by 180°C over 20 minutes. As suspected, it did not quite reach the target temperature because the temperature started to drop off around 100°C instead of 150°C, as the program expected. This should be an easy adjustment, since it is just a matter of increasing the duration of the cycle at an earlier time.
My two corrections ended up being huge overshoots. The drop off time (100°C) is correct, but the default rate increase that worked in the other cases is not working at all here.
The goal of "v2.X test #3" is to heat the hot plate to 200°C over the course of 20 minutes, and with v2.6, I have effectively succeeded. There will likely be more issues once I try, for example, to heat the hot plate to 300°C over the course of 60 minutes, but for now, I want to stick with lower temps and shorter times while I work out the kinks. Now that I understand the difficulties of PWMing a hot plate, adapting the code to combat future issues should be straightforward.
To summarize my code, I control the heating rate by cycling the hot plate's power on and off for some % of 1000ms. In other words, the hot plate is on 300ms then off 700ms then on 300ms etc., where the relation between target heating rate and hot plate on time is based on previously gathered data. This produces a nice, linear(ish) temperature increase up until a certain temperature, at which point it plateaus. In the previous versions, the way I compensated for this was by increasing the on time by 5ms for every cycle after 150°C. This did not work for slower heating rates, so the newer versions changed this by making the 5ms and 150°C varry depending on the target heating rate. The exact value is a linear extrapoliation from previous data. This is imperfect, but I do not think perfection will ever be possible with the current equipent, and I think I have reached something good enough that now I can finally apply it to my optically contacted samples.
Since I have finished this "stage" of work, for completeness, I am including all of the code, data*, and graphs involved so far.
*the .txt data files are in the cycle_vX_graphs folders; these folders also have the Jupyter notebooks I used for graphing the data
I realized that, after changing so much from v2.3 to 6, I should check that my first two tests produce correct results with the latest version. This was good because all three tests turned out to be innaccurate, as they were all short roughly 10°C. However, they were very precise. For all three, the final temperature was 193.15±1.5°C.
Since I was focusing on the hot plate code and therefore did not need my weights, I decided to leave them on top of my samples for roughly 2 weeks.
It appears that an increased amount of time under pressure does not result in any noticable differences. A slight increase in surface area (SA) in two places, and a slight decrease in SA in another place, but overall no change. Note that "(initally)" in the picture below refers to http://nodus.ligo.caltech.edu:8081/Mariner/89.
Now that I have (relatively) good PWM code, I wanted to do my first real test with actual samples. Since everything went smoothly, I will now work on building the original set up for the project, which included attaching thermocouples to two plates so we could precisely measure the heat between them.
As you can see in the pictures below, I am running an Arduino off of my laptop which controls an AC/DC control replay that turns the AC power to the hot plate on and off.
Firstly, last night's heating did not change the contacted surface area greatly, but there is too many factors to speculate as to why that is the case. I leave that for future testing.
I attached the thermocouples by adhering them to the two aluminum plates. I was careful to make sure that the thermocouple was in the dead center of the aluminum plate. The other end of the thermocouples—exposed positive and negative wires—were screwed into the K Type connector so they can be plugged into the thermometer/multimeter. Taking the average between the top and bottom plate will give a more precise estimate of the temperature of the samples.
I intended to test the new thermocouple set up today, but when I plugged them in, both did not read a temperature. It took me a long time to figure out what went wrong: when installing the K Type thermocouple connector, the wires of the thermocouple need to be pushed in as far in as possible, otherwise the circuit would not be completed. It took a lot of trial and error to figure this out. I first created a test "circuit" with wire and a resistor to make sure that the connector itself was not broken. Then I carefully observed how moving the wires in different places affected the reading.
Once I did carefully reassemble the thermocouples, they worked perfectly, as indicated by the non-zero current. I ran tests with my three thermocouples and two devices to see how precise the temperature reading is. The results are below and pictures of the readings can be found in the zip file. I cannot explain why one of the adhered thermocouples is hotter than the other.
Plate #1 and 2 refers to the two different aluminum plates. T1 and T2 refers to the two ports on the Digital Thermometer 343. It cannot read two thermocouples simultaneously (as far as I can tell); it's so one can be used as a baseline/reference value for the other.
Since the two devices are giving different temperature readings, I would like to find out if this imprecision is linear (e.g. they are always 3°C off, so I just need to add/subtract 3°C after taking the measurements). If not, some sort of calibration is probably required. I decided to figure this out by running the heating tests I did before, but this time with the plates. This also serves as a test to see how the plates heat up.
Or rather, this is what I would have done, had I not realized that the thermometers were going down as the heat was increaing, meaning I had switched the polarity for both thermocouples. It turns out that this mix-up is a common mistake. I thought that I double checked that red was positive for thermocouples, but it is in fact not:
"red is the usual color for positive charges, whereas the red wire in thermocouple cables typically contains the negative signal. This coloration is ANSI standard for thermocouples, but it is not what most people expect."
I performed the same tests I have been doing prior (+180°C in 10 minutes) but now with the (correctly wired) thermocouples attached to the metal plates. The top plate is thermocouple #1 attached to the Fluke and the bottom plate is thermocouple #2 attached to the TPI (the lime green one).
The base heating rate for the new set up will require some tweaking to the code because the plates heat up much slower, but as I have mentioned previously, I do not think this will require a lot of extra work since I now know the tips and tricks to PWMing the hot plate. The only difficulty might come from the increase in hysteresis (i.e. the plates continue to increase in the temperature long after it turns off). For future tests, I need to remember to continue recording the temperature after program finishes its 10 min cycle.
On the positive, I think this test shows that taking the average of the two thermocouples to find the temperature in the center (where the optically contacted samples are) is a worthwhile endevor, considering how much the top plate lags behind the bottom plate in terms of heating speed.
With v3.0, I took a couple steps backwards by getting rid of the feature that increases the heating rate so I can isolate the base heating rate for the two plates. In my experience, the best way to figure out how to modify the program is to try a bunch of different target temperatures and heating times and look for correlations. I started with (attempting) to increase the plates by 280°C in 10 minutes.
For a future release, I am thinking of radically (relatively speaking) changing the function parameters: the user only inputs the target heating rate and how long the plates should be heated at this rate. This is to address the hysteresis in this new set-up, which I will elaborate on if I make the change.
I decided test how fast the plates would heat up if the heat was just on constantly on for 5 minutes. In general, these tests are raising a lot of questions in regards to controlling the temperature given the hysteresis in the system. It is also apparent that the bottom plate heats up signficantly faster than the top one, which means I need to heat the samples much longer than, say 10 minutes, if I want to avoid unevenly heating both parts of the optically contacted piece.
I also have to be conscientious that I am already half way through the quarter and ideally should be devoting time to bond strength testing rather than continuing to fiddle with the hot plate.
To combat the bottom plate heating up much faster than the top plate, I decided to try increasing the cycle period from 1000ms (1s) to 10000ms (10s). In other words, taking the test I today ran as an example, the hot plate will now be on for 1000ms then off for 9000ms then repeat. Hopefully this should give more time for the heat to transfer to the top plate, but even in this short test, it still appears to be a problem.
Due to the slower heating times, this will be a bit more challenging to test as each test could take hours to complete, but this is more in line with the final intended use anyways. Perhaps my cycle of 1000ms on is too much (e.g. I should do 100ms on then 9900ms off, although I think that might be so slow that it will never heat up; this also raising the question as to how I will deal with mantaining this slow heat up at the higher temperatures).
[I'm behind on data processing, but I'm creating an entry on the day I actually run the tests]
[I'm (once again) behind on data processing, but I'm creating an entry on the day I actually run the tests]
The Arduino / AC PWM interface looks good. I recommend that you maintain the code in GitHub and post a link to the repo whenever you update the code. Use detailed commit messages so that it makes sense.
For the plotting, it would be good if you can use grid lines and markers for the data points. Then we can see the difference between the data and the fits, etc.
And to avoid the hysteresis, etc. you can record the temperature in your Arduino and use feedback to make the heater just go to whatever temperature you specify. So you would have a prescribed T(t) and the PID feedback loop would just make the heater take you there. Can your Arduino read the thermocouple?
Attached is a cartoon partial view into the heat load experienced by the Mariner assembly.
The omnigraffle file with more explicit arrow labelling in the 'layers' tab is available here. The dashed red lines along to top represent vacuum chamber radiation incident on all sides of the OS/IS, not just from the top. Off picture to the right is the BS, left is the beam tube/ETM chamber -- hence the lower absored laser power (solid line) absorbtion (PR power + no HR coating absorption).
Missing or wrong
*Note: the current modeling script can be found at: CryoEngineering/MarinerCooldownEstimation.ipynb
Nina pointed me to the current mariner cooldown estimation script (path above) and we have since met a few times to discuss upgrades/changes. Nina's hand calculations were mostly consistent with the existing model, so minimal changes were necessary. The material properties and geometric parameters of the TM and snout were updated to the values recently verified by Nina. To summarize, the model considers the following heat sources onto the testmass (Pin):
- laser absorption by ITM bulk (function of incident laser power, PR gain, and bulk absorption)
- laser absorption by ITM HR coating (function of incident laser power and HR coating absorption)
- radiative heating from room-temp tube snout (function of snout radius and length, and TM radius)
The heat transfer out of the testmass (Pout) is simply the sum of the radiative heat emitted by the HR and AR faces and the barrel. Note that the script currently assumes an inner shield T of 77K, and the inner/outer shield geometric parameters need to be obtained/verified.
Nina and Paco have been working towards obtaining tabulated emissivity data as a function of temperature and wavelength. In the meantime, I created the framework to import this tabulated data, use cubic spline interpolation, and return temperature-dependent emissivities. It should be straightforward to incorporate the emissivity data once it is available. Currently, the script uses room-temperature values for the emissivities of various materials.
- Incorporate tabulated emissivity data
- Verify and update inner/outer shield dimensions
How about a diagram so that we can understand what this model includes?